J. D. Vance

Eight-year climatology of nocturnal temperature and sodium density in the mesopause region (80 to 105 km) over Fort Collins, Co (41°N, 105°W)

Based on 417 nights of lidar observation between 1990 and 1999 at Fort Collins, CO (41°N, 105°W), we tabulate an eight-year composite of monthly mean temperatures and Na densities in the mesopause region, and plot the associated altitude/month contours. The maximum and minimum mean mesopause temperatures were 192 K at 101 km and 178 K at 85.5 km on the 294th and 164th days of the year, respectively. The maximum and minimum monthly mean layer temperatures between 83 and 105 km were 205.8 K and 188.8 K, respectively, in November and July. When the episodic warming that peaked in 1993 is removed, the mean temperatures are typically lowered by ∼4 K. Climatology supports a two-level thermal structure with mesopause occurring at higher altitudes in winter and lower altitudes in summer, and sharp transitions between them taking place in May and August. The maximum and minimum mean peak sodium densities were 4.88 × 109 m−3 at 91 km and 1.49 × 109 m−3 at 90 km on the 310th and 163rd days of the year, respectively.

Continuous-wave, all-solid-state, single-frequency 400-mW source at 589 nm based on doubly resonant sum-frequency mixing in a monolithic lithium niobate resonator

Sum-frequency mixing of two cw single-mode Nd:YAG lasers in a doubly resonant congruent lithium niobate resonator generated two TEM(00) beams of single-frequency 589-nm radiation. The primary beam had a power of 400 mW and the secondary beam of approximately 15 mW by use of 320 mW of 1319-nm and 660 mW of 1064-nm Nd:YAG radiation incident on the lithium niobate resonator. This corresponds to an optical power conversion efficiency of more than 40%.

Continuous-wave sodium D2 resonance radiation generated in single-pass sum-frequency generation with periodically poled lithium niobate.

With two cw single-mode Nd:YAG lasers at 1064 and 1319 nm and a periodically poled lithium niobate crystal, 11 mW of 2 kHz/100 ms bandwidth single-mode tunable 589 nm cw radiation has been detected using single-pass sum-frequency generation. The demonstrated conversion efficiency is approximately 3.2%[W(-1) cm(-1)]. This compact solid-state light source has been used in a solid-state-dye laser hybrid sodium fluorescence lidar transmitter to measure temperatures and winds in the upper atmosphere (80-105 km); it is being implemented into the transmitter of a mobile all-solid-state sodium temperature and wind lidar under construction.

Sodium lidar measurements of waves and instabilities near the mesopause during the DELTA rocket campaign

The sounding rocket for the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign was successfully launched from Andoya at 00:33 UT on Dec 13, 2004. Though it was cloudy at the time of launch, theWeber Na lidar was operating intermittently between 20:00 UT and 23:30 UT on Dec 12, observing Na density, temperature and meridional wind between 80 and 100 km. Throughout the lidar observations, we observed significant small (λz < 5 km) and medium-scale (λz ≈8–15 km) wave activity producing significant wind and temperature shears. There were unusually large (up to 10 m/s and 10 K amplitudes) perturbations of the vertical wind and temperature profiles at 21 UT with a 3 km vertical wavelength that was much stronger in the vertical beam than in the north beam. The atmosphere appeared to become more active as the launch time approached. During the last interval with data, at ∼23:20 UT, Dec. 12th, the lidar profiles revealed a gravity wave in both beams with a magnitude of 5–10 K in temperature and approximately 5 km vertical wavelength. The large background shear plus the wave perturbation produced regions with potential convective instability at multiple altitudes.

High-resolution lidar experiment for the Thirty Meter Telescope

Adaptive optics (AO) systems of next generation optical ground telescopes will employ laser guide stars (LGS) to achieve wide sky coverage. In these systems the mesospheric sodium layer at ~ 90 km height is excited by means of laser-induced fluorescence of the Na I D2 resonance hyperfine transmission. The finite thickness of sodium layer, and temporal variations in its density structure, result in LGS that are elongated and have internal structure that varies with time. This degrades the performance of the AO system due to degeneracy between effects of atmospheric and sodium layer variations. In order to quantify this and assess the impact on future extremely large telescopes such as the Thirty-Meter Telescope (TMT), measurements are needed of the density distribution of the sodium layer with high spatial and temporal resolution. We describe the design of a new lidar experiment to investigate the spatio-temporal power spectra of the Na-variations at frequencies as high as 50 Hz. This system employs a 5 W pulsed laser and a 6 m liquid mirror telescope, which provide sufficient sensitivity for high-resolution studies. The transmitter is a YAG-pumped dye laser, with an optical collimation system that allows the beam divergence to be controlled over a range from diffraction-limited to several arcmin. This will also allow the investigation of saturation effects, important for the next generation high power LGS systems. Backscattered photons will be collected at the prime focus using four high-efficiency photomultiplier detectors and a fast counting system. The resulting system will provide vertical density profiles with a spatial resolution as small as 2 m.